An epidemiologic study of idiopathic dilated cardiomyopathy (DCM) is proposed with the overall objectives of identifying risk factors for this poorly understood cause of heart failure in young adults, using newly diagnosed cases (n=150) ascertained from Washington, D.C. area hospitals and neighborhood controls (n=300), and examining prognostic factors among the cases alone over a follow-up period of two to three years. The specific aims are: 1) To determine whether the reported association between idiopathic DCM and history of asthma can be confirmed, and to investigate the possible role of medications used in the treatment of asthma in the etiology of idiopathic DCM, 2) To examine possible associations between idiopathic DCM and history of cigarette smoking, moderate alcohol consumption, and diabetes mellitus, 3) To clarify the importance of hypertension in the development of idiopathic DCM, and 4) To examine the prognostic importance of selected environmental exposures and clinical and hemodynamic parameters with respect to survival and major cardiovascular complications. A matched case-control design will be utilized to accomplish the first three specific aims. The medical records of possible cases of idiopathic DCM who are discharged from five acute hospitals over a two year accrual period will be abstracted so that standard diagnostic criteria may be applied. Two neighborhood controls will be identified for each verified case using a random digit dialing technique. The cases and controls will be matched on five year age intervals, sex, and telephone exchange. The subjects or a close relative will be interviewed by telephone using a structured questionnaire. To accomplish the fourth specific aim, the cases will be contacted on an annual basis during the two to three year follow-up period to determine their vital status and experience with respect to major cardiovascular complications. Additional data will be collected from health care providers using mailed questionnaires in order to validate information obtained from the subjects by interview. Statistical analysis will consist of case-control comparisons using conditional logistic regression techniques, and survival analyses using Kaplan-Meier curves and the proportional hazards model. Thus, the study will provide important new data about the determinants of idiopathic DCM, and about prognostic factors, which may assist in the prevention and treatment of this increasingly important disease.